Battery-operated systems may operate as battery-operated sub-systems operating within larger battery-operated systems. One example includes an automobile. An automobile relies on a battery for its electrical power. The automobile may include electronic systems that also rely on their own battery for electrical power. Such electronic systems may be built into the automobile, or optionally added after the automobile has been assembled. The battery may be added to power the battery-powered sub-system to avoid overloading the main system battery, or to be able to provide the sub-system as optional equipment that is added later.
Certain military vehicles use doors that have layers of armor built in to withstand enemy fire and other combat environment hazards. The armor adds a substantial amount of weight to the door often making them difficult for a user to open or close the vehicle doors. Powered door systems may be added to such doors to provide a powered mechanism to assist in opening or closing the doors. Such powered mechanisms may include an electric motor (such as a DC motor), a hydraulic drive, or a pneumatic drive.
The powered door systems may be controlled by an electronic controller. The electronic controller and the powered mechanism may use the military vehicle's battery as a source of power. However, this may overload the vehicle battery. A secondary battery may be added to power powered door system. In battery powered systems, such as a military vehicle, that include a battery-powered sub-system, such as the powered door system, the primary battery may be connected to the secondary battery to enable charging the secondary battery.
The connection between the batteries may need to be controlled, and the secondary batteries may need to be sufficiently recharged. A controller may be used to switch the batteries into different modes for charging and for providing power.
In some applications, such as in military vehicles, the batteries may be subjected to extreme conditions that may affect the battery performance. For example, military vehicles may operate in extreme cold. Some batteries perform better than others at low temperatures. For example, low energy density lead-acid batteries perform better at low temperatures than higher energy density batteries. However, because lead-acid batteries have a low and relatively fixed energy density, their size is directly related to their capacity. As a result, the size of lead-acid batteries increases as their capacity increases. For certain applications, the size of lead-acid batteries can become prohibitively large.
High energy density batteries are alternatives to lead-acid batteries. Because of the high energy density in these batteries, similar capacities can be achieved in smaller sizes. Such high energy density batteries include: nickel metal hydride (NiMH) batteries; nickel-cadmium (NiCd) batteries; and lithium-ion (L-ion) batteries. However, these high energy density batteries do not perform well at low temperatures, and experience performance degradation much faster than their lead-acid counterparts. As a result of these space and temperature requirements, it is desirable to have a high energy density battery that can maintain a reasonable power output at low temperatures. One solution is to heat the high-density batteries.
There are several known methods of heating the battery. The battery may be heated by external power dissipated in an external enclosure—heating blanket. This method requires a source of external energy, which may not be available. In addition this method is not energy efficient, because some of the energy is dissipated into the environment. The battery may be heated by charging, which also requires an external energy source. The battery may also be heated by alternative current, which may circulate almost lossless between the battery and an energy tank—inductor, or between two batteries via energy mediator—also inductor. These two methods require much less energy to warm the battery, because the actual warming is happening inside the battery by chemical reaction during charging and discharging. The necessity of self-heating mode may arrive, when no other source of energy besides the battery itself is available. Those skilled in the art will know that a self-warmed battery performs much better than a cold battery, even if the battery has wasted part of its charge on warming.
Accordingly, there is a need for a way to efficiently charge and heat a battery in battery-operated systems that include battery-operated sub-systems.